In addition to providing printed telephone directories, telephone companies provide information services to their subscribers. The services may include stock quotes, directory assistance and many others. In most of these applications, when the information requested can be expressed as a number or number sequence, the user is required to enter his request via a touch tone telephone. This is often aggravating for the user since he is usually obliged to make repetitive entries in order to obtain a single answer. This situation becomes even more difficult when the input information is a word or phrase. In these situations, the involvement of a human operator may be required to complete the desired task.
Because telephone companies are likely to handle a very large number of calls per year, the associated labour costs are very significant. Consequently, telephone companies and telephone equipment manufacturers have devoted considerable efforts to the development of systems which reduce the labour costs associated with providing information services on the telephone network. These efforts comprise the development of sophisticated speech processing and recognition systems that can be used in the context of telephone networks.
In a typical speech recognition system the user enters his request using isolated word, connected word or continuous speech via a microphone or telephone set. The request may be a name, a city or any other type of information for which either a function is to be performed or information is to be supplied. If valid speech is detected, the speech recognition layer of the system is invoked in an attempt to recognize the unknown utterance. In a first pass search, a fast match algorithm is used to select the top N orthographies from a speech recognition dictionary. In a second pass search the individual orthographies are re-scored using more precise likelihood calculations. The top two orthographies in the re-scored group are then processed by a rejection algorithm that evaluates if they are sufficiently distinctive from one another so that the top choice candidate can be considered to be a valid recognition. However the accuracy of these systems, especially when designed for connected word recognition may not be always acceptable.
Thus, there exists a need in the industry to refine the speech recognition process such as to obtain a better recognition system with a high degree of accuracy particularly applicable to connected word recognition systems.